US Patent 7297921 Photodetection circuit and confocal microscope that has it

A first amplification unit amplifies at a predetermined amplification rate an output signal from a photodetection unit for detecting an optical signal from a specimen and detecting it. An offset unit assigns offset to an output signal from the photodetection unit. A second amplification unit amplifies at an amplification rate smaller than the amplification rate of the first amplification unit an output signal from the photodetection unit assigned the offset by the offset unit. A rectification unit rectifies an output signal from the second amplification unit. An addition unit adds an output signal from the first amplification unit to an output signal from the rectification unit.